Many commercial parking lots or parking structures have separate entry lanes or roadways for automobiles and separate exit lanes. To prevent unauthorized entry through the exit lane it is common to provide hinged teeth that normally incline toward an incoming vehicle, but incline away from an outgoing vehicle. An outgoing vehicle drives over the spikes, whereupon they rotate to a horizontal position and the exiting automobile is not damaged. An automobile entering the exit the wrong way runs into the inclined spikes, which do not rotate further, thus puncturing the tires of such automobiles. The threat of tire damage is very visible, and such traffic controllers are very effective in preventing unauthorized entry.
The projecting spikes, however, present a safety hazard to pedestrians, including children at play, persons having sight impairment, and nighttime pedestrians. Not only are pedestrians tripped by the spikes, sustaining injury from a fall, but persons who fall on the spikes might well sustain fatal puncture wounds.